Paul writes: The Black-veined White (Aporia crataegi) is a large striking-looking butterfly which used to occur in England but became extinct here around 1925. It was generally a fairly localised species mainly in southern England but occurred as far north as Yorkshire. It is still uncertain why it became extinct because its main foodplants, Hawthorn and Blackthorn, are abundant. Several suggestions such as poor summers, predation by birds and increased use of pesticides have been made. Re-introduction has also been tried and failed, including attempts by Winston Churchill in the 1940’s.
It is widespread and fairly common on mainland Europe. I see them quite regularly on holiday over there. This pair were seen in July in the Swiss Alps.